[SCSI] zfcp: Fix oops when port disappears

The zfcp_port might have been removed, while the FC fast_io_fail timer
is still running and could trigger the terminate_rport_io callback.
Set the pointer to the zfcp_port to NULL and check accordingly
before using it.

Reviewed-by: Martin Petermann <martin@linux.vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
diff --git a/drivers/s390/scsi/zfcp_fsf.c b/drivers/s390/scsi/zfcp_fsf.c
index 3f365ac..74dee32 100644
--- a/drivers/s390/scsi/zfcp_fsf.c
+++ b/drivers/s390/scsi/zfcp_fsf.c
@@ -172,12 +172,16 @@
 					 struct fsf_link_down_info *link_down)
 {
 	struct zfcp_adapter *adapter = req->adapter;
+	unsigned long flags;
 
 	if (atomic_read(&adapter->status) & ZFCP_STATUS_ADAPTER_LINK_UNPLUGGED)
 		return;
 
 	atomic_set_mask(ZFCP_STATUS_ADAPTER_LINK_UNPLUGGED, &adapter->status);
+
+	read_lock_irqsave(&zfcp_data.config_lock, flags);
 	zfcp_scsi_schedule_rports_block(adapter);
+	read_unlock_irqrestore(&zfcp_data.config_lock, flags);
 
 	if (!link_down)
 		goto out;